title: Accumulation of K-Ras codon 12 mutations in the F344 rat distal colon following azoxymethane exposure.
abstract: Azoxymethane (AOM) administration to F344 male rats is a widely used model of human colon carcinogenesis. The current study investigates quantitatively the accumulation of K-Ras codon 12 mutations following AOM exposure. Male, 6-week-old F344 rats were treated subcutaneously with 30 mg/kg body weight of AOM, and colon tissue was collected at 1, 8, 24, and 32 weeks after treatment. The K-Ras codon 12 GGT to GAT and GGT to GTT mutant fractions (MFs) were measured using allele-specific competitive blocker polymerase chain reaction (ACB-PCR). Between 1 and 32 weeks after AOM treatment, the K-Ras codon 12 GGT to GAT geometric mean MF in the rat colon increased significantly from 12.9 × 10(-5) to 145 × 10(-5) , and the GGT to GTT geometric mean MF increased significantly from 5.26 × 10(-5) to 180 × 10(-5) . K-Ras codon 12 GGT to GAT MF also increased significantly in AOM-treated rat colon tissue at 1 week compared to controls (4.44 × 10(-5) ). The accumulation of the GGT to GAT MF long after the DNA adduct repair phase suggests that a portion of cells containing this mutation have a proliferative advantage, allowing them to accumulate as nascent tumors progress. Also, the GGT to GAT background MF increased in untreated rats, indicating that there is accumulation with age. The ACB-PCR assay generates quantitative data of cancer-related mutations and thus provides insight into pathological processes following carcinogen exposure.
authors.affiliation: Division of Genetic and Molecular Toxicology, National Center for Toxicological Research, Jefferson, Arkansas 72079, USA. page.mckinzie@fda.hhs.gov
authors.forename: Page B
authors.initials: PB
authors.lastname: McKinzie
authors.forename: Barbara L
authors.initials: BL
authors.lastname: Parsons
mesh_terms: D000818:Animals; D001397:Azoxymethane / Q000633:toxicity*; D003062:Codon / Q000235:genetics*; D003106:Colon / Q000187:drug effects* / Q000378:metabolism*; D011905:Genes, ras / Q000235:genetics*; D008297:Male; D009154:Mutation / Q000235:genetics; D016133:Polymerase Chain Reaction; D051381:Rats; D011916:Rats, Inbred F344
chemical_list: D003062:Codon; D001397:Azoxymethane